Description

The experimental data were taken from
(1) D. T. Halfen and L. M. Ziurys, 2018, Phys. Chem. Chem. Phys. 20, 11047.
The cyclic molecule can be viewed as a C2 molecule somewhat loosely bound to an Al atom. Only transitions with even Ka are allowed because of symmetry. The spectroscopic parameters differ somewhat from those in (1). The A rotational parameter was taken from
(2) J. Yang, R. H. Judge, and D. J. Clouthier, 2011, J. Chem. Phys. 135, Art. No. 124302.
Only transitions with Ka = 0 were observed in (1). Therefore, transitions with higher Ka cannot be predicted reliably. In addition, redictions should be viewed pwith caution above 130GHz.
The dipole moment was taken from an ab initio calculation in (2).